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The system bus provides the wearable computer with a flexible connectivity interface through which the majority of external devices can communicate and draw power. Such devices include the GPS Interface board, Accelerometer Interface board, electronic compass interface and a HP Jornada Handheld PC.
Two versions of the bus exist, the first, a prototype that was developed on vero-board which is compatible with all 3 existing wearable motherboards, whereas the second and most recent design is a Bitsy only interface PCB that is really intended for the new cyber-jacket.
Prototype Design Notes
A block diagram of the first prototype is shown below:
The prototype bus interface board can optionally provide the wearable motherboard with raw (14V) or filtered (5V) power from a pair of Sony Lithium-Ion batteries (NP-F750) that are connected to the bus device cable
Furthermore, the bus has been designed such that it is compatible with the following wearable motherboards:
whereby compatibility is achieved through the use of a motherboard specific cable that mates the bus interface board to the various ports and connectors on each motherboard. The initial bus schema (by Cliff Randell) can be found here which is associated with the following GC+ pinout (other pinouts omitted since they are unlikely to be used in future) :
A pseudo vero-board (NOT PCB) layout is available for this prototype and is shown below. The source vector file can be found here for which you will need 'ExpressPCB' (installed on Prawn) or for download here.
Production Design Notes (Bitsy Only)
Schematic / PCB
A PCB layout is available for the production board and is shown below. The source vector file can be found here for which you will need 'ExpressPCB' (installed on Prawn) or for download here.
Prototype System Bus Interface board with GC+ mating cable assembly.
Bitsy Interface board PCB (bare).
Bitsy motherboard with interface board stacked on top (coin = 5p).